Field of the Invention
The present invention relates to an image forming apparatus provided with a drive transmission mechanism for transmitting drive to a driven unit, such as a cartridge.
Description of the Related Art
Recent years have seen a requirement for image forming apparatuses, such as copying machines, laser beam printers and inkjet printers, to be capable of forming images of high definition. Therefore, the resolution of an image formed on a sheet is improved by improvement of the toner and/or intermediate transfer belt, etc. Here, there are cases where rotational non-uniformities occur in rotating bodies, such as the photosensitive drum and developing roller.
A rotational non-uniformity means a variation in the angular velocity of rotation of the rotating body. There are cases where density non-uniformities occur in the image formed on a sheet, due to the occurrence of rotational non-uniformities in the photosensitive drum, developing roller, and the like. A density non-uniformity means that the density of the image formed on the sheet is not constant.
When a very slight rotational non-uniformity has occurred in the photosensitive drum, or the like, the density non-uniformity caused in the image is often so small as to be imperceptible. However, with the recent increase in image resolution, even if a very small rotational non-uniformity has occurred in the photosensitive drum, or the like, this may be perceptible as a density non-uniformity in the image. The causes of rotational non-uniformities are considered to be eccentricity in the rotating bodies, such as the photosensitive drum, the developing roller and the gears.
Eccentricity occurs in a rotating body due to divergence or inclination, etc. of the rotational center axis of the rotating body, which means that driving force is not transmitted accurately from the drive source to the rotating body and variations may occur in the angular velocity of rotation of the rotating body. In other words, it is necessary to reduce rotational non-uniformities in order to suppress density non-uniformities occurring in the image.
In order to resolve this problem, in Japanese Patent No. 3211780, bearings which support a rotary shaft of a gear that transmits drive to a photosensitive drum, or the like, and a frame which supports the bearings, are formed integrally. More specifically, burring is provided on a metal frame, and by using the burring as the bearings, the rotational accuracy of the gear is improved. If the frame and bearings are formed as separate members, then the rotational accuracy of the gear deteriorates due to error in the positioning of the bearings with respect to the frame.
However, by unifying the frame and bearings in an integrated body, it is possible to improve the rotational accuracy of the gear, accordingly, without the occurrence of any positioning errors of the bearings with respect to the frame. Here, in Japanese Patent No. 3211780, a process cartridge having a rotating body, such as a photosensitive drum, is positioned in a frame that is separate from the frame in which the burring is formed. The frame in which the burring is formed, and the frame in which the process cartridge is positioned are then coupled by screws, or the like.
Furthermore, conventionally, a drive transmission mechanism 100 such as that shown in FIG. 7 is known. The drive transmission mechanism 100 has a frame 101, a bearing 102, a drive transmission member 106 and a drive coupling member 107. Drive which is transmitted to the drive transmission member 106 from drive means (not illustrated) is transmitted to the drive coupling member 107, and is transmitted to a supply roller 115 from the drive transmission member 106 via the drive receiving member 111. The drive coupling member 107 which transmits the drive to a driven unit 110 is supported rotatably by a bearing 102 attached on the frame 101.
However, in Japanese Patent No. 3211780, a process cartridge having a rotating body, such as a photosensitive drum, is positioned in a frame that is separate from the frame in which the burring is formed. Therefore, the rotational accuracy of the photosensitive drum, and the like, provided in the process cartridge, declines to the extent that error occurs in the positioning of the frame in which the process cartridge is supported and the frame in which the burring is formed. Consequently, there is a risk of density non-uniformities in the image formed on the sheet.